providing a test transmitter, and moving it to one or more selected sites within existing cells of the system; the transmitter transmitting test signals to mobile stations within its vicinity, the mobile stations within the vicinity transmitting first signal strength response signals to said test signals, and said mobile stations transmitting second signal strength response signals to corresponding test signals from base stations of associated cells;
and analyzing received first and second response signals for assessing traffic density within the vicinity of the transmitter, comprising analyzing the received first signal strength response signals to determine those first response signals which are greater than a predetermined threshold value, and comparing those first response signals which are greater than a predetermined threshold value with the second signal strength response signals to determine the value of the first response signals in relation to the second response signals.
[0001] This application claims priority of European Patent Application No. 99310353.0, which was filed on Dec. 21, 1999.
[0002] The present invention relates to the location of traffic, in particular regions of increased traffic density, in mobile cellular telecommunications systems.
[0003] When a new network operator is licensed and the network designed, the radio base stations are usually planned on the basis of providing maximum coverage with relatively low traffic capacity. In this way, the new service is made available to the maximum number of possible consumers, as rapidly as possible, while minimizing the initial capital outlay. The radio network planning at this stage is satisfactorily performed with a combination of manual field strength surveys from test transmitters, and automatic coverage prediction and frequency assignment software.
[0004] Once the new network's subscriber base grows, it becomes necessary to add traffic capacity, often in the form of additional base station sites. It is at this stage that it is necessary to identify areas of traffic congestion, and target the provision of new base station sites in these areas. Thus, the location of regions of increased traffic density or “hot spots” is an important problem, particularly for the siting of base transceiver stations (BTS) to accommodate the traffic. Many such “hot spots” can be identified by careful analysis of geographical/morphological data and good knowledge of the area. However, there remains a great interest in the automation of such process.
[0005] It is an object of the present invention to provide a method and means for automatically assessing the traffic density in geographical regions in a mobile cellular telecommunications system.
[0006] In a first aspect, the present invention provides a method for assessing traffic density in a mobile cellular telecommunications system, the method comprising:
[0007] providing a test transmitter means, and moving it to one or more selected sites within existing cells of the system;
[0008] the transmitter means, at the or each site, transmitting test signals to mobile stations within its vicinity,
[0009] the mobile stations within the vicinity transmitting first response signals to said test signals, and said mobile stations transmitting second response signals to corresponding test signals from base stations of associated cells;
[0010] and analyzing received first and second response signals for assessing traffic density within the vicinity of the transmitter means.
[0011] In a second aspect, the present invention provides apparatus for assessing traffic density in a mobile cellular telecommunications system, comprising:
[0012] a test transmitter means, movable to one or more selected sites within existing telecommunications cells and arranged to transmit test signals to mobile stations within its vicinity; which mobile stations are arranged to transmit first response signals to said test signals;
[0013] and means for analyzing received first response signals, in addition to received second response signals to corresponding test signals from base stations of associated cells, for assessing traffic density within the vicinity of the transmitter means.
[0014] The present invention is particularly preferred for use with the GSM system, but other systems may be employed for example UMTS, AMPS, TACS, NMT, etc. In the specification below, where acronyms are used without an explanation, they have the meaning assigned to them by the relevant ETSI standards for the GSM system.
[0015] In accordance with the invention, a transmitter of low power is used, so that only mobile stations (MS) in the vicinity of the transmitter detect the signal. The nature of the test signal will naturally depend on the type of mobile system in which the invention is used, since the test signals must be compatible with those received by existing base transceiver stations (BTS). As preferred, the test signal is such that the mobile stations make signal strength reports, constituting said first response signals, at regular intervals of the type used for handover operations between cells. However the response signals may comprise other parameters, as for example the signal delay between signals transmitted from a BTS and received by a mobile station.
[0016] The present invention may be used for different purposes:
[0017] “hot spot” detection, in order to identify the best location for micro cells (typically 100 m-200 m radius) or pico cells (typically 50 m radius).
[0018] Global traffic map generation, in order to predict congestion problems and plan cost effective capacity enhancements.
[0019] Interference area location, as part of the network optimisation process.
[0020] Global interference map generation, which could then be used in automatic frequency planning tools.
[0021] In a preferred form of the present invention, a mobile base transceiver station (BTS) is used to assess the traffic in its small coverage area. The mobile BTS is located in the area under study with a small coverage area (low transmit power). For accuracy the coverage area is checked, via drive test or field strength prediction tools to determine the likely size of cell. Then the traffic generated in that area is measured.
[0022] There are three ways of measuring the traffic:
[0023] 1. If the mobile BTS is an active cell in the network, the traffic can be measured using OMC (operation & maintenance centers) counters.
[0024] 2. The mobile BTS is an active cell but the “Directed Retry” feature is activated for it. From the OMC a report is retrieved to review the total number of MS being diverted to other cells for further call establishment.
[0025] 3. The mobile BTS is a passive cell, i.e. broadcasts in one frequency but it is barred so that it cannot accept calls. The BTS is set as neighboring cell of the surrounding cells so that mobiles measure its signal (to do that mobile stations need to decode the FCCH and SCH (frequency correction and synchronization channels), so a dummy transmitter is not possible), that is then reported to the BSC (base station controller). Analysis of measurements allows discrimination of traffic that is generated in the foot print of the BTS.
[0026] Thus in accordance with the invention, for solutions 1 and 2, the test transmitter constitutes the serving cell for mobile stations, and said associated cells constitute the neighboring cells of the serving cells. For solution 3 however, said associated cells constitute the cell serving the mobile stations and neighbouring cells of the serving cell.
[0027] The first solution is quite complex because base station parameters such as handover thresholds and neighbor lists have to be configured, not only for the micro base station, but for the surrounding ones, and they might require new tuning every time the mobile station is moved. With the first and second solutions, there is the added complexity of needing a way to connect the base station to its BSC, probably via microwave links. This might be completely impossible in some situations and is in general impractical.
[0028] Therefore, the third solution is preferred. In addition to the passive mobile BTS, for measurement recording, an A
[0029] This third solution is very well suited to identify the best possible location for micro or pico cells in the case of “hot spot” relief, especially if the area under consideration has been limited using preliminary manual techniques. Further, it permits the invention to be implemented with a minimum of additional equipment, requiring merely a test transmitter, a protocol analyzer, and software for analyzing the results provided by the protocol analyzer.
[0030] As preferred, said method for analyzing test results comprises analyzing a first set of test results to determine those first response signals which are greater than a predetermined threshold value, and analyzing a second set of test results to compare those first response signals which are greater than a predetermined threshold value with the second response signals to determine the value of the first response signals in relation to the second response signals.
[0031] In a third aspect, the present invention provides a method, for assessing traffic density in a mobile cellular telecommunications system, by analyzing test results obtained from a test procedure involving a test transmitter making test transmissions, and mobile stations within its vicinity making first response signals to said test transmissions, and second response signals to corresponding transmissions made by the base stations of associated cells,
[0032] received versions of the first response signals constituting a first set of test results and received versions of the second response signals constituting a second set of test results,
[0033] said method for analyzing test results comprising analyzing said first set of test results to determine those first response signals which are greater than a predetermined threshold value,
[0034] and analyzing said second set of test results to compare those first response signals which are greater than a predetermined threshold value with the second response signals to determine the value of the first response signals in relation to the second response signals.
[0035] In a fourth aspect, the invention provides apparatus, for assessing traffic density in a mobile cellular telecommunications system, by analyzing test results obtained from a test procedure involving a test transmitter making test transmissions, and mobile stations within its vicinity making first response signals to said test transmissions, and second response signals to corresponding transmissions made by the base stations of associated cells,
[0036] received versions of the first response signals constituting a first set of test results and received versions of the second response signals constituting a second set of test results,
[0037] said apparatus comprising means for analyzing said first set of test results to determine those first response signals which are greater than a predetermined threshold value, and
[0038] means for analyzing said second set of test results to compare those first response signals which are greater than a predetermined threshold value with the second response signals to determine the value of the first response signals in relation to the second response signals.
[0039] In a preferred embodiment, received versions of the first and second response signals are forwarded from base stations to a BSC, and an A
[0040] A preferred embodiment of the invention will now be described with reference to the accompanying drawings, wherein:
[0041]
[0042]
[0043] FIGS.
[0044] Referring to
[0045] The received signal strength of the test transmitter, as reported by MS in the vicinity, and sent to their serving BTS, are then forwarded via 2 Mb/s circuits
[0046] The intercepted measurement reports are analyzed by HSD (Hot Spot Detector) software
[0047] Prior to commencing the measurement report analysis, an initial test procedure is carried out to manually identify likely areas of localized traffic congestion, where it may be feasible to deploy an additional cell. This activity is based on a combination of the following techniques: location of existing BTSs that become congested during busy hours; visual inspection of maps showing areas of increased usage, e.g. shopping centers.; comparison of above maps with coverage predictions from existing BTS sites, etc.
[0048] Once an initial attempt has been made to identify hot spot locations, a number of possible test positions are identified. Several test positions S
[0049] In order to record measurement results, the test transmitter
[0050] The test transmitter
[0051] Integral antenna, with external antenna connector (45-55□),
[0052] Internal battery, with run time >1 Hr,
[0053] Optional external DC PSU,
[0054] Transmit power 0.1-0.5 W, +/−2.5 dB
[0055] Operating frequency, three different units for either,
[0056] 935-960 MHz, or,
[0057] 1805-1880 MHz, or,
[0058] 1930-1990 MHz.
[0059] Transmits GSM channels,
[0060] Frequency Correction Channel (FCC),
[0061] Synchronization Channel (SCH),
[0062] Broadcast Control Channel (BCCH).
[0063] Configuration
[0064] Although the test transmitter configuration will, to some extent, be dependent on the settings and channel assignment used in the existing mobile network, the basic test transmitter set-up is given below.
[0065] Frequency Correction Channel (FCCH),
[0066] The Absolute Radio Frequency Channel Number (ARFCN) is set to a channel that the existing network operator is licensed to use, and is not simultaneously in use in the vicinity of the test site.
[0067] Synchronization Channel (SCH),
[0068] The SCH carries the Base Station Identity Code (BSIC),
[0069] It comprises two octal digits, First, the Network Color Code (NCC) which is set to that of the existing network, Second, the Base station Color Code (BCC) which can be set to a number that identifies it from the surrounding base stations in the test area.
[0070] Broadcast Control Channel (BCCH),
[0071] The BCCH carries the Global Cell Identity (GCI) number that is comprises two elements, Cell Identity (CI), Location Area Identity (LAI), that is itself formed from three numbers: Mobile Country Code (MCC), Mobile Network Color Code (MNCC), and Location Area Code (LAC),
[0072] Transmit Power,
[0073] The test transmitter output power is set according to the coverage range that is required, and the type of external power amplifier that may be used,
[0074] The output power takes a value within the range +20 to +27 dBm (+/−2.5 dB),
[0075] The required transmit power can be estimated by:
[0076] Identifying the test area,
[0077] Using coverage prediction software (and field strength measurement results if available) to estimate the field strength that is received in the test area from the existing cells in the vicinity,
[0078] Using coverage prediction software (and field strength measurement results if available) to estimate the field strength that is received in the test area from the test transmitter, and raise it to such a level that it is the strongest signal in the test area.
[0079] Cell Access Barring,
[0080] The test transmitter is set as ‘Barred’, to prevent mobiles from attempting to use the cell, and thereby delay their access to the existing network.
[0081] Broadcast Control Channel (BCCH),
[0082] The System Information (SI) is transmitted on the BCCH,
[0083] If the BCCH is switched ‘Off’, then only the FCH and SCH are transmitted,
[0084] Provided that the ‘Cell Barring’ is set ‘On’, then the BCCH can be set ‘On’ for the purpose of the HSD test.
[0085] BCCH Allocation (BA) List,
[0086] The BA list is used to broadcast a list of the neighbor cells to the mobiles in the vicinity,
[0087] This facility is not used for the HSD test, and the ‘BA List’ can be set ‘Off’.
[0088] Identification of Test Transmitter
[0089] It is necessary for the HSD software
[0090] The HSD software supports two means of test transmitter identification:
[0091] Using a unique Network Color Code (NCC) element of the BSIC number assigned to the test transmitter, and entering it in the HSD software ‘New Test Transmitter’ dialogue box,
[0092] Entering the test transmitter ‘BCCH_FREQ_NCELL(i)’ value (associated with the ARFCN that is used by the test transmitter), in the HSD software ‘New Test Transmitter’ dialogue box.
[0093] BSC
[0094] The BSC software has to be configured such that the existing BTS in the test area broadcast the identification information relating to the test transmitter to mobiles in the area.
[0095] For mobiles in the vicinity of the test transmitter to include signal level measurements for the test transmitter in their measurement reports to their serving cell, it is necessary for the test transmitter to be included as a neighbor cell in the BA list transmitted by the serving cell.
[0096] This is achieved by making the following changes:
[0097] Create a new (dummy) BTS to represent the test transmitter, together with its associated Handover Control Object, and Power Control Object.
[0098] Modify the neighbor cell lists broadcast by the existing BTSs in the test area, to include the dummy BTS as a valid neighbor cell
[0099] HSD Software
[0100] Referring to
[0101] Analysis Parameters:—User enters parameters that are used in the calculation.
[0102] Measurement Time:—User enters start and finish date of the test, as well as the start and finish time of the measurement. The start and finish time is used as a filter for the timestamp entries in the source Abis log file.
[0103] Antenna:—Antenna specific data is entered.
[0104] Lat./Long. Location:—The user enters the latitude and longitude location of test transmitter.
[0105] Process Log File Button:—Upon selection the source Abis Log File is processed.
[0106] Default Values Button:—Upon selection all dialog fields are populated with default values.
[0107] View Result Button:—Upon selection the user is returned to the main interface window and can view the result of the current analysis.
[0108] View Source Log File Button:—Upon selection the source file is opened and printed in the dialog window.
[0109] The Analysis Results Window is where all the calculation results are presented to the user. This comprises the following:
[0110] Output test file name:—The path and directory of the output test transmitter output file.
[0111] %1:—% of measurement report for which the test transmitter signal level was above the user defined threshold, as amended by the power correction factor
[0112] Time 1:—Total no. of Test Transmitter measurements above threshold×0.48 Seconds.
[0113] %2:—% of measurement report for which the test transmitter signal level was above the user defined threshold, as amended by the power correction factor, and is received as Best Server.
[0114] Best Server is taken to mean Test Transmitter received at a higher level than the current server and all the neighbor cells.
[0115] Time 2:—Total no. of Test Transmitter measurements as Best Server, above threshold×0.48 Seconds.
[0116] TNM:—Total Number of Valid Measurements.
[0117] The results are explained in the following table:
Parameter Definition Percentage of Test Transmitter The percentage of measurement that test RXLEV measurements above transmitter has RXLEV above threshold threshold Call time in Test Transmitter The call time that test transmitter has RXLEV measurements above RXLEV above threshold. It is obtained threshold by multiplying 0.48 seconds by the number of test transmitter RXLEV measurements that are above threshold. Percentage of Test Transmitter The percentage of measurement that test RXLEV measurements are the transmitter has the highest RXLEV best server among the serving cell and all other neighbour cell. Call time in Test Transmitter The call time that test transmitter is the RXLEV measurements are the best server. It is obtained by multiplying best server 0.48 seconds by the number of test transmitter measurements in which it is the best server.
[0118] The HSD algorithm is depicted the flow chart of FIGS.
[0119] Step
[0120] Step
[0121] Step
[0122] Step
[0123] Step
[0124] Step
[0125] Step
[0126] Step
[0127] Step
[0128] Step
[0129] Step
[0130] Step
[0131] For the second part of the algorithm, this part of the algorithm is constructed for the calculation process. The data used in the calculation are extracted from the selected A
[0132] Referring to
[0133] Step
[0134] Step
[0135] The channel description includes:
[0136] A
[0137] A
[0138] A
[0139] U
[0140] U
[0141] U
[0142] Step
[0143] Step
[0144] Step
[0145] Step
[0146] Step
[0147] The extracted data consist of,
[0148] The measurement time,
[0149] The channel description,
[0150] The measurement number,
[0151] The DTX downlink status (DTX represents voice operated switch control for the MS),
[0152] The measurement valid,
[0153] The serving cell RXLEV (full and sub),
[0154] The top six neighbor cells information in terms of signal strength measurements. For each neighbor cell, the value of RXLEV, BCCH, NCC and BCC are recorded.
[0155] Step
[0156] Step
[0157] Step
[0158] Step
[0159] Step
[0160] Step
[0161] Step
[0162] Step
[0163] Step
[0164] Step
[0165] Step
[0166] Step
[0167] Referring to
[0168] Step
[0169] Step
[0170] Step
[0171] Step
[0172] Step
[0173] Step
[0174] Step
[0175] Referring to
[0176] Step
[0177] Step
[0178] Step
[0179] Step
[0180] Step
[0181] Step
[0182] Step
[0183] Step
[0184] Step
[0185] Step
[0186] Step
[0187] Step
[0188] Step
[0189] Step
[0190] Step
[0191] Step
[0192] Step
[0193] Step
[0194] Step
[0195] Referring to
[0196] Step
[0197] Step
[0198] Step
[0199] Step
[0200] Step
[0201] Step
[0202] Step
[0203] Step
[0204] Step
[0205] Step
[0206] Step
[0207] The END PROCEDURE is the final step of the calculation part. The output of this procedure is the results that the user will be shown. The HSD software calculation algorithm produces four result values
[0208] The percentage of measurement reports within the analysis time window, for which the test transmitter received signal level (plus user entered power correction factor) is above the (user entered) signal level threshold.
[0209] The time in seconds, within the analysis time window, for which the test transmitter received signal level (plus user entered power correction factor) is above the (user entered) signal level threshold.
[0210] Each measurement report accounts for approximately 0.48 s.
[0211] The percentage of measurement reports within the analysis time window, for which the test transmitter received signal level (plus user entered power correction factor) is
[0212] Above the (user entered) signal level threshold, and,
[0213] Is the best server (i.e. is received at a higher level than either the serving or neighbor cells).
[0214] The time in seconds, within the analysis time window, for which the test transmitter received signal level (plus user entered power correction factor) is
[0215] Above the (user entered) signal level threshold, and,
[0216] Is the best server (i.e. is received at a higher level than either the serving or neighbor cells).
[0217] The following points should be considered when the HSD results are analyzed.
[0218] The ‘Call Seconds’ values can only be used for comparison purposes if either:
[0219] The A
[0220] The HSD analysis time window is set to extract the same length of time from each A
[0221] The ‘Call Seconds’ value can be used to gain a good indication of the volume of traffic that could be served from each test site.
[0222] The ‘Percentage’ value can be used to check how well the test site compares with the current serving site.
[0223] The ‘Best Server’ values can be used as an indication as to the extent to which traffic would be switched to the test site; however it should be borne in mind that:
[0224] The test transmitter EIRP, and Power Correction Factor must be set such that the test site is representative of an actual BTS installed at the site,
[0225] The power threshold level is set at the required received power level for the service area,
[0226] If the test transmitter antenna position is not the same as that of the intended BTS installation, the coverage will differ to some extent (even though the power correction factor may be applied).
[0227] Modifications may be made to the preferred embodiment as follows:
[0228] Support the use of multiple test transmitters,
[0229] Dual band operation with two transmitters at one location,
[0230] Multiple transmitters at different locations,
[0231] Analyze the effect of selecting multiple new BTS sites.